Engines may be configured to deliver fuel to an engine cylinder using one or more of port and direct injection. Port fuel direct injection (PFDI) engines are capable of leveraging both fuel injection systems. For example, at high engine loads, fuel may be directly injected into an engine cylinder via a direct injector, thereby leveraging the charge cooling properties of the direct injection (DI). At lower engine loads and at engine starts, fuel may be injected into an intake port of the engine cylinder via a port fuel injector, reducing particulate matter emissions. During still other conditions, such as under heavy load, a portion of fuel may be delivered to the cylinder via the port injector while a remainder of the fuel is delivered to the cylinder via the direct injector. During such conditions, fuel is required from both the PFI system and the DI system to maintain a desired combustion air-fuel ratio.
However the inventors herein have identified a potential issue with PFDI systems. If the port fuel injection system stops functioning during engine operation, such as due to port injector circuit issues, the engine may be damaged due to prolonged lean combustion. Specifically, the engine control system may not respond rapidly enough when the port fuel injection system stops functioning while the direct fuel injection system continues to operate to meet the operator torque demand. As a result, engine airflow may continue to be provided based on the total fuel flow to provide engine torque, resulting in a leaner than desired combustion. Prolonged lean combustion can result in misfires and engine damage. In contrast, in PFI only systems, when the port injection system is degraded, there is zero torque in the cylinder and the engine control system is able to respond to the zero torque condition.
In one example, the above issue may be at least partly addressed by a method for an engine comprising: responsive to an indication of port injector degradation, received while fueling a cylinder via each of a port and a direct injector, limiting an intake air flow. In this way, engine degradation due to discontinuation of port fuel injection in a PFDI system may be reduced.
As one example, an engine may be configured with each of port and direct fuel injection capabilities. During conditions when the engine is being fueled via each of port and direct injection, engine air flow may be adjusted based on the total fuel flow from the fuel injectors to provide a desired combustion air-fuel ratio (e.g., stoichiometric air-fuel ratio). Responsive to an indication of degradation of the PFI system, such as due circuit degradation of a single port injector or due to a loss of electrical power to the port injection system, a direct injection fuel schedule may be adjusted, if possible, to compensate for the loss of port injected fuel. For example, a direct injection pulse-width may be extended, if possible, to compensate for at least a portion of the port injected fuel that was supposed to be delivered, thereby providing as much of the torque as possible. In addition, engine air flow may be limited by reducing an opening of an intake throttle and/or via cam timing adjustments. In particular, the engine air flow limit may be determined based on the amount of fuel delivered via direct injection only, while ignoring the desired/commanded port injector flow. For example, the opening of the intake throttle may be reduced to be commensurate with (or a function of) the updated direct injection fuel pulse-width so that the desired combustion air-fuel ratio (e.g., stoichiometric air-fuel ratio) is maintained.
In this way, by limiting an engine air flow in a PFDI engine system responsive to an indication of port injection fuel system degradation, unintended lean combustion may be reduced. By adjusting an intake throttle position based only on the direct injected fuel flow, and independent of the desired (or anticipated) port injected fuel flow, air flow may be appropriately limited responsive to the discontinuation of port injected fuel flow. By limiting the air flow to maintain engine operation at a desired combustion air-fuel ratio despite the degradation of the PFI system, engine performance and life may be extended.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.